1. Field of the Invention
The present invention relates to an electric actuator which makes it possible to allow a slider to reciprocate linearly along an actuator body, and a method of assembling the same.
2. Description of the Related Art
An electric actuator has been hitherto used, in which a workpiece placed on a slider is transported to a predetermined position by displacing the slider along an actuator body by a motor.
The conventional electric actuator of this type has a frame. Functional elements mounted on the frame include a driving force-transmitting section (e.g., a ball screw shaft or a timing belt), a guide section (e.g., a linear guide rail or a guide block), and a table unit. A cover, which closes the opening of the frame, is also provided in order to protect the internal structure of the frame.
The rigidity of the electric actuator is principally secured by the frame. In order to secure a high rigidity, it is necessary to enhance the geometrical moment of inertia of the frame. This means that a sufficient frame dimension is secured in a direction in which the rigidity of the frame is required. If the sufficient dimension is not secured, the wall thickness of the frame may be increased, for example, thus the increase in weight is inevitable.
When a variety of functional elements are arranged on the frame as described above, the direction of the rigid support means for the functional structure (direction in which the frame extends) is restricted. Therefore, for example, it is necessary to provide an auxiliary support member such as a bearing-holding structural member (housing). Further, a cover is required to protect the internal structure and the environment. When the auxiliary support member and the cover as described above should be provided, the entire weight of the electric actuator is increased, which relatively results in the decrease in rigidity since the weight to be supported by the frame is increased.
Further, when a variety of functional elements are arranged on the frame, the location of the frame is limited at a specified portion in the cross section. That is, the frame affects the support function and the attachment function for the entire electric actuator. Therefore, when the direction of attachment of the frame is limited to perform the operation in a desired position (e.g., in a lateral position or a cantilever position), it is necessary to provide, for example, a frame support means such as a bracket in order to support the frame. As a result, the overall rigidity is decreased, and the weight and dimension are increased.
The stress from the workpiece and the frame concentrates on the frame support means such as a bracket. Therefore, there is a need to use elements that are capable of withstanding the concentration of stress.